Microencapsulation of probiotics (Lactobacillus acidophilus and Lactobacillus rhamnosus) in raspberry powder by spray drying: optimization and storage stability studies

Non-dairy probiotic foods are becoming popular because they do not pose problems of lactose intolerance and high cholesterol content while they offer an alternative from traditional sources and for personal preferences. The shelf life of probiotic products requires to maintain viability as high as > 106-108 CFU/unit. To tackle these aspects, the microencapsulation of probiotics in a raspberry juice powder by spray drying was studied. A combination of probiotics (Lactobacillus acidophilus NRRL B-4495 and Lactobacillus rhamnosus NRRL B-442) was chosen to maintain high viability along with multiple health benefits. The chosen microencapsulating agent- maltodextrin's role as carbon source was also assessed (in an MRS recipe) for its prebiotic potential. High temperatures employed during spray drying are detrimental to the probiotics and can be circumvented by sub-lethal thermal shock (50°C for L. acidophilus and 52.5°C for L. rhamnosus) before spray drying. Optimization of the process through response surface method was performed. Inlet temperature (°C), total solids: maltodextrin ratio, and inlet feed rate (mL/min) were fixed as independent variables while % recovery, % survival and color (ΔE-total color change) were the dependent outputs. The optimized model with all the significant factors had an overall desirability of 0.91. Storage study of the raspberry encapsulated probiotic powder was performed in glass containers stored at room and refrigerated temperatures for 30 days. CFU/g, water activity, color (powder and rehydrated liquid) were analyzed throughout the storage period. Since the CFU numbers do not necessarily correlate with functionality, basic probiotic characteristic tests like acid and bile tolerance and antibiotic sensitivity assay were performed before spray drying and after 30 days storage. At the end of storage, the three best responses with respect to % viability retention at cold and room temperature were chosen for electron image analysis of the microspheres. The optimized model was obtained at the following conditions: inlet temperature of 100°C, Maltodextrin ratio of 1:1 and inlet feed rate of 40 mL/min.;Keywords: sub-lethal effect, microencapsulation, optimization.